1. Field of the Invention
The present invention relates to an internal combustion engine with an ignition plug and a vehicle provided with the same.
2. Description of the Related Art
In spark ignition type internal combustion engines having an intake opening for suction of an air-fuel mixture and an exhaust opening for exhaust of combustion gases, it has been conventionally thought to be preferable to arrange an ignition plug around a center of a combustion chamber, that is, in the vicinity of a cylinder axis in order to improve the anti-knock property. Actually, however, parts other than an ignition plug are provided in an internal combustion engine, and an adequate anti-knock property cannot necessarily be obtained only by simply arranging an ignition plug in the vicinity of a cylinder axis while neglecting the layout of these other parts. It has been proposed to arrange an ignition plug to be offset toward an intake opening from a cylinder axis (see, for example, FIG. 7 of U.S. Pat. No. 5,027,761).
When an ignition plug is arranged offset toward an intake opening as in U.S. Pat. No. 5,027,761, a space on a side of the intake opening becomes smaller than the ignition plug on a cylinder head. As a result, when the amount of offset of the ignition plug toward the intake opening is large, the amount of open area of the intake opening must be decreased. When the open area of the intake opening is increased, however, a decrease in intake quantity is caused, so that a reduction in engine output occurs.